1. Field of the Invention
The present invention relates to a process of hydraulic seaming together of layers of nonwoven fabrics in one or two directions at a time.
2. Prior Art
Spunlacing or hydroentanglement using water jets has been used to combine layers of filament or fiber webs in continuous processes for many years. Layers of webs are manufactured using most standard spunlace equipment disclosed in prior process patents describing entangling systems, such as in Evans U.S. Pat. No. 3,485,706, incorporated begin by reference.
Hydroentangled nonwovens produced in roll form are used in the further manufacture of many products ranging from complex articles such as clothing to less complex items such as filters, filtration bags, pillow ticking, upholstery backing, etc. Bonding in selected areas is generally involved in the production of products. Seam formations used to join layers together are normally made by sewing, by use of adhesives, by thermal bonding, or by ultrasonic sewing.
Sewing produces a strong joint but is typically a slow process and leaves behind minute separations at the thread joints. Thermal bonding is suited to high speeds and automated systems but nonwovens made of certain non-thermoplastic materials, such as cotton or rayon cannot be thermally bonded due to their intrinsic characteristics. Thermal seaming of thermoplastic fabrics typically results in a stiff seam, since the seam line is like a weld. Adhesive bonding adds to the cost of the fabric due to the raw materials and additional processing equipment and processes. Further, adhesive seams can also be stiff, depending upon the type of adhesive utilized. Ultrasonic bonding or sewing has speed limitations and its efficiency is greatly influenced by the basis weight of the fabrics. Also, ultrasonic sewing is subject to the same fabric thermal property limitations as thermal bonding.
There is limited discussion in the art on using water jets to join fibrous webs together in a selected pattern. U.S. Pat. No. 4,970,104 describes using a hydroentangling process to pattern bond previously unbonded fibrous batts, as an alternative to thermal pattern bonding. U.S. Pat. No. 3,514,455 refers to the manufacture of a quilted batting where a thermally bonded polyester continuous filament fabric is joined to a staple fiber batt by means of an all over pattern of spot bonding by water jets. The quilting is achieved by forming closely spaced parallel rows of hydraulically formed xe2x80x9cstitchesxe2x80x9d along the length of the stacked layers in the direction of travel of the fabric along a belt of a machine used to create the parallel rows of stitches.
The production of load bearing seams, such as for garment or upholstery manufacture, requires a significantly stronger seam than required for spot bonding or quilting. Preparation of quilt padding is intended primarily to hold layers in proximity and prevent interlayer slippage and bunching. Seams in apparel and upholstery are required to withstand significant stresses, applied in multiple directions, without failure.
To date there has not been proposed a process for seaming together in the direction of travel and/or in the cross direction two layers of nonwoven fabric, with the seams being suitable for use in an environment requiring softness and suppleness of the seam, in combination with a suitable degree of strength of the bond, such as when an end seam is formed in, for example, a pillow case.
According to the invention there is provided a process for seaming together at least two layers of nonwoven fabric, with the individual layers being prebonded. Manufacture of the seams is contemplated for both the direction of travel of the webs in the seaming process and/or in the cross direction, as the webs are passed through a hydroentangling station. It is an aspect of the invention that the seams produced are sufficiently strong as to withstand the stresses and tensions normal to construction seams in anticipated end use applications. It is a further aspect of the invention that the seams thus provided would be soft and supple and free of any holes, needle marks, fused areas or chemicals. It is a still further aspect of this invention that the seam width and design would be infinitely variable and that the seams would be produced continuously. It is yet another aspect of this invention that adjacent product pieces defined by the seam perimeters could be separated from each other in a continuous or batch cutting or slitting process where the seam lines provide the cut lines for such processing.
In another aspect of the invention, a nonwoven fabric assembly is provided, in which the assembly comprises at least a pair of superimposed layers of consolidated nonwoven fabrics. The assembly comprises at least one line of seam between the layers, with the seam being characterized by a concentrated and continuous line or sector of entanglement of the fibers between the fabrics, providing a durable and high strength seam, which can exceed the tensile strength of the fabric. The seam is additionally characterized as being highly flexible and devoid of any other extraneous bonding aids, such as thread, adhesives, and relatively stiff thermal bonds. Typically, seams of the present invention would preferably occupy less than about 10% and most preferably 5% of the surface area of at least one of the joined fabric layers. The remainder of the surface area of the joined layers would generally be free of seams or constructive stitches according to the methods described for the invention.